/*
   * linux/fs/nfs/cache_lib.c
   *
   * Helper routines for the NFS client caches
   *
   * Copyright (c) 2009 Trond Myklebust <Trond.Myklebust@netapp.com>
   */
  #include <linux/kmod.h>
  #include <linux/module.h>
  #include <linux/moduleparam.h>
  #include <linux/mount.h>
  #include <linux/namei.h>

  #include <linux/slab.h>

  #include <linux/sunrpc/cache.h>
  #include <linux/sunrpc/rpc_pipe_fs.h>
  
  #include "cache_lib.h"
  
  #define NFS_CACHE_UPCALL_PATHLEN 256
  #define NFS_CACHE_UPCALL_TIMEOUT 15
  
  static char nfs_cache_getent_prog[NFS_CACHE_UPCALL_PATHLEN] =
  				"/sbin/nfs_cache_getent";
  static unsigned long nfs_cache_getent_timeout = NFS_CACHE_UPCALL_TIMEOUT;
  
  module_param_string(cache_getent, nfs_cache_getent_prog,
  		sizeof(nfs_cache_getent_prog), 0600);
  MODULE_PARM_DESC(cache_getent, "Path to the client cache upcall program");
  module_param_named(cache_getent_timeout, nfs_cache_getent_timeout, ulong, 0600);
  MODULE_PARM_DESC(cache_getent_timeout, "Timeout (in seconds) after which "
  		"the cache upcall is assumed to have failed");
  
  int nfs_cache_upcall(struct cache_detail *cd, char *entry_name)
  {
  	static char *envp[] = { "HOME=/",
  		"TERM=linux",
  		"PATH=/sbin:/usr/sbin:/bin:/usr/bin",
  		NULL
  	};
  	char *argv[] = {
  		nfs_cache_getent_prog,
  		cd->name,
  		entry_name,
  		NULL
  	};
  	int ret = -EACCES;
  
  	if (nfs_cache_getent_prog[0] == '\0')
  		goto out;
  	ret = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
  	/*
  	 * Disable the upcall mechanism if we're getting an ENOENT or
  	 * EACCES error. The admin can re-enable it on the fly by using
  	 * sysfs to set the 'cache_getent' parameter once the problem
  	 * has been fixed.
  	 */
  	if (ret == -ENOENT || ret == -EACCES)
  		nfs_cache_getent_prog[0] = '\0';
  out:
  	return ret > 0 ? 0 : ret;
  }
  
  /*
   * Deferred request handling
   */
  void nfs_cache_defer_req_put(struct nfs_cache_defer_req *dreq)
  {
  	if (atomic_dec_and_test(&dreq->count))
  		kfree(dreq);
  }
  
  static void nfs_dns_cache_revisit(struct cache_deferred_req *d, int toomany)
  {
  	struct nfs_cache_defer_req *dreq;
  
  	dreq = container_of(d, struct nfs_cache_defer_req, deferred_req);
  
  	complete_all(&dreq->completion);
  	nfs_cache_defer_req_put(dreq);
  }
  
  static struct cache_deferred_req *nfs_dns_cache_defer(struct cache_req *req)
  {
  	struct nfs_cache_defer_req *dreq;
  
  	dreq = container_of(req, struct nfs_cache_defer_req, req);
  	dreq->deferred_req.revisit = nfs_dns_cache_revisit;
  	atomic_inc(&dreq->count);
  
  	return &dreq->deferred_req;
  }
  
  struct nfs_cache_defer_req *nfs_cache_defer_req_alloc(void)
  {
  	struct nfs_cache_defer_req *dreq;
  
  	dreq = kzalloc(sizeof(*dreq), GFP_KERNEL);
  	if (dreq) {
  		init_completion(&dreq->completion);
  		atomic_set(&dreq->count, 1);
  		dreq->req.defer = nfs_dns_cache_defer;
  	}
  	return dreq;
  }
  
  int nfs_cache_wait_for_upcall(struct nfs_cache_defer_req *dreq)
  {
  	if (wait_for_completion_timeout(&dreq->completion,
  			nfs_cache_getent_timeout * HZ) == 0)
  		return -ETIMEDOUT;
  	return 0;
  }
  
  int nfs_cache_register(struct cache_detail *cd)
  {

  	struct vfsmount *mnt;

  	struct path path;

  	int ret;
  
  	mnt = rpc_get_mount();
  	if (IS_ERR(mnt))
  		return PTR_ERR(mnt);

  	ret = vfs_path_lookup(mnt->mnt_root, mnt, "/cache", 0, &path);

  	if (ret)
  		goto err;

  	ret = sunrpc_cache_register_pipefs(path.dentry, cd->name, 0600, cd);
  	path_put(&path);

  	if (!ret)
  		return ret;
  err:
  	rpc_put_mount();
  	return ret;
  }
  
  void nfs_cache_unregister(struct cache_detail *cd)
  {
  	sunrpc_cache_unregister_pipefs(cd);
  	rpc_put_mount();
  }